Abstract
ABSTRACT Although nickel (Ni) is recognized as plant nutrient since the turn of the 21st century, uncertainty remains about its optimum application rates and forms. This paper focuses on Ni application in soils, relating to its effect as a plant micronutrient. Specifically, the effect of Ni on the activity of urease in soybean plants is examined. The effects of applying four Ni rates in two different soil types were tested. A full factorial 2 × 4 blocked design experiment was established under controlled conditions. Ni rates (0, 0.25, 0.5 and1.0 mg of Ni·kg–1 of soil) were applied in two soils with contrasting clay contents. The addition of Ni increased the urease activity in soybean plants but was affected by soil textural differences. The highest urease activity was achieved by the application of 1.0 mg·kg–1 Ni in the sandy soil. The absorption of Ni by the plants and its availability was found to be soil texture dependent. The rate of 0.25 mg·kg–1 Ni increased the soybean dry matter production by 25% in the sandy soil. In conclusion, Ni was effective in promoting plant growth and biomass accumulation although depending on soil clay proportion. For soybean, there was no correlation between urease activity and biomass accumulation. The results of this study indicate a clear Ni effect in different type of soils in Sao Paulo state, serving as a solid initial doses indicator for soybean fertilization programs and future studies on nickel in Soybean.
Highlights
Soybean is one of the most important crops in the world, as it constitutes a major source of protein for both animal and human food, in addition to its recent use as a feedstock for the manufacture of biofuels (Alovisi et al 2011). soybean is one of the most produced grain crops in the world, the average yield in many countries, such as Brazil, can still be considered low with increased production possible through a better understanding of its nutritional requirements
It is important to note that the sandy soil contained almost no Ni and the control was not supplemented to reach the same content of clayey soil (Table 2)
This point alone is of agronomic significance as it can be hypothesized that in this area of Brazil soybean grown on sandy soil becomes deficient in Ni if and when the seed reserves of Ni are depleted
Summary
Soybean is one of the most important crops in the world, as it constitutes a major source of protein for both animal and human food, in addition to its recent use as a feedstock for the manufacture of biofuels (Alovisi et al 2011). soybean is one of the most produced grain crops in the world, the average yield in many countries, such as Brazil, can still be considered low with increased production possible through a better understanding of its nutritional requirements. Ni has an important function in nitrogen metabolism (Brown and Sunderman Jr. 1980) due to its structural and functional role on urease, the enzyme that breaks down urea to CO2 and NH4+ (Dixon et al 1975; Bai et al 2006). As regards to the Ni fraction within urease, Fabiano et al (2015) reported that besides urease, Ni can activate an isoform of glyoxalase I, which performs an important role in the degradation of a potent cytotoxic compound – methylglyoxal. This fact suggests that Ni may play an important role in the metabolism of antioxidants in plants, especially under stress
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